Digital information transmitted in frame switched data networks is included in chronologically successive, transmittable data frames. The information contained in a data frame can be coarsely divided into overhead data and payload data. Overhead data includes for example a frame start field, i.e. a synchronizing word by which the starting point of a frame in a transmitted bit flow can be detected. Payload data includes data connected to the utilization of services enabled by the data network, as well as data connected to the operation control and management of the data network. Services enabled by a data network are for instance Internet bank services, electronic shopping services, and electronic data search services. Payload data typically represents an information unit or part of an information unit, produced by a protocol of a higher hierarchy level that uses the transmission service offered by the frame switched data transmission protocol. Said frame switched data transmission protocol can be for example an Ethernet protocol, and said information unit can be for example an IP (Internet Protocol) packet. For instance in a data frame according to the Ethernet protocol, the overhead data is represented by an eight-byte preamble, a six-byte destination address, a six-byte source address, a two-byte frame type detector and a four-byte cyclic redundancy check. In the present document, the term “byte” refers to a group of eight bits, i.e. a bit octet. Payload data carried by an Ethernet frame is placed in a frame data field, the size of which is at least 46 bytes. In case said payload data is less than 46 bytes, the rest of the minimum sized frame data field is filled with padding bits. The Ethernet protocol is described for example in the technical specification IEEE802.3 (Institute of Electrical and Electronics Engineers). In order to be able to utilize the transmission capacity of the data network as effectively as possible, the payload data should be arranged in successive data frames, so that the share of overhead data of all data to be transmitted should be as small as possible, i.e. the share of payload data of all data to be transmitted should be as large as possible.